docs: replace legacy line‑dot‑left‑horizontal icons with unified dot icon across docs

apps/docs/content/(01-linear-structures)/stack/155-min-stack.mdx

@@ -1,7 +1,7 @@
 ---
 title: '155. Min Stack'
 description: Design a stack that supports push, pop, top, and retrieving the minimum element in constant time
-icon: line-dot-left-horizontal
+icon: dot
 sidebar:
   label: 'Min Stack'
   badge: 'Medium'